FLEA FACTS ARE REAL HEAD-SCRATCHERS

Fleas, infamous as household pests, are veritable Olympians among insects.

Fleas of various species can:

- Jump 150 times their own length, vertically or horizontally, equivalent to a man jumping nearly 1,000 feet. A rat flea was clocked jumping 30,000 times without stopping.- Accelerate 50 times faster than the space shuttle after liftoff.

- Survive months without feeding.

- Withstand enormous pressure, the secret to surviving the scratchings and bitings of the flea-ridden.

- Remain frozen for a year, then revive.

"Preparing for liftoff, the flea crouches like a runner waiting for the gun," author-photographer Nicole Duplaix writes in the current National Geographic. Leg and thorax muscles compress a tiny pad of superelastic protein in the thorax known as resilin. A complex mechanism triggers the explosive release of resilin energy that hurls the flea upward.

Highly specialized bloodsucking parasites, fleas evolved at least 60 million years ago, probably living on prehistoric mammals. Fleas' ancestors may have had wings, but these would have tangled in the host's fur.

Jumping provided an alternative means of reaching a passing host or evading enemies. Muscles and tendons were gradually modified to help power the formidable hind legs that make the flea a star performer.

But these remarkable creatures have a darker side. As carriers of plague, fleas have claimed more victims than all the wars ever fought.

Three plague epidemics, so vast they were called pandemics, ravaged the world, Duplaix writes, killing more than 200 million people. Only disease-carrying mosquitoes have caused as much misery.

The first pandemic in A.D. 541 swirled around the Mediterranean Sea in a deadly maelstrom for more than two centuries, killing as many as 40 million people and weakening the Byzantine Empire. At its peak in Constantinople, one historian reported, the plague killed 10,000 people a day.

The second pandemic came in the 14th century with the opening of lucrative trade routes across Asia. In 1347, vessels sailed into Sicily with crews dying from a mysterious disease. No one noticed that shipboard rats were also ill.

The next five years were so devastating that they became known as the time of the Black Death. By 1352, in Europe alone, 25 million people had died.

The sweeping plague reshaped European society. With few serfs left to till the land, survivors could negotiate for wages with landlords. The breakdown of manorialism and the evolution of a money-based economy sowed the seeds of capitalism.

In the late 1800s, the third pandemic spread plague around the world. It lingers today. Carried out of China in 1855, plague reached Hong Kong by 1894, killing some 10,000 people. Steamships now carried the disease even faster to places where it had been unknown: Japan, Australia, southern Africa and the Americas.

Six million died in India in a decade. In a makeshift laboratory in Bombay, Paul-Louis Simond of France's Institut Pasteur dissected rats and found the plague bacillus. Fleas engorged with contaminated rat blood, he observed, could transmit plague from rat to rat or, through a bite, from rat to man.

Today, perhaps only 120 of the 2,400 known species and subspecies of fleas can transmit plague. Fewer than 20 species readily bite man.

In 1986, the World Health Organization tallied 1,003 cases of plague, but many countries fail to report the disease. In the United States last year, there were 12 cases and two deaths.